Natural gas is an important fuel gas and it is used extensively as a basic raw material in the petrochemical and other chemical process industries. The composition of natural gas varies widely from field to field. Many natural gas reservoirs contain relatively low percentages of hydrocarbons (less than 40%, for example) and high percentages of acid gases, principally carbon dioxide, but also hydrogen sulfide, carbonyl sulfide, carbon disulfide and various mercaptans. The acid gases are detrimental to hydrocarbon handling and usage, and therefore acid gases are typically removed from the produced hydrocarbons by processes that are well known. The natural gas may also contain inert gases such as nitrogen, which are also removed by methods that are well known. The separated acid gas and inert gas often has insufficient value to justify further treatment or purification for any further commercial usage. “Waste gas” is a term that will used in this patent to describe a gas containing acidic components such as hydrogen sulfide or carbon dioxide, and may or may not contain inert gases. The waste gas typically has little or no commercial value.
Proposals have been made to re-inject the separated waste gas into disposal strata through an injection well directly into a depleted or spent zone of the hydrocarbon-bearing formation from which the gas was produced (see for example U.S. Pat. No. 5,267,614) or re-injected into a separate subterranean strata (see for example U.S. Pat. No. 6,149,344 and World Intellectual Property Organization publication number WO 00/58603). However, the prior art does not address how to simultaneously produce a gas while re-injecting a waste gas into the same formation.
There is a need for an improved method of more efficiently and effectively producing natural gas and at the same time disposing of waste gases into the same formation.